The present invention relates to a novel electrode material, more particularly to an electrode material that is made of a carbonaceous material having a specific pseudographite structure and electron state and which is capable of making a lightweight and non-polluting electrochemical cell having high energy and maximum power densities.
In order to meet the recent requirement for using less energy in industries and to make the most of the rapid progress of electronic devices, it is strongly desired to develop new batteries which are light in weight and small in size and which produce great electromotive force and exhibit high maximum power and energy densities.
The present invention provides an electrode material suitable for use as battery electrodes. When positive and negative electrodes made of the material of the present invention are submerged in a liquid electrolyte, an electromotive force can readily be generated by applying an external voltage so that the positive electrode is doped with negative ions, and the negative electrode with positive ions. Thereafter, the electrodes are connected to an external load and a current is caused to flow by removing the respective ions from the positive and negative electrodes. This cycle of doping ions and removing them can be used as electrochemical charge and discharge reactions in the battery.
A battery may also be constructed by using one electrode which is made of the material of the present invention and the other electrode made of a known material.
The use of carbonaceous materials as electrode materials is already known. For example, it is reported in J. Electrochem. Soc., 125, 687 (1978) that when metallic lithium is used as the negative electrode and graphite as the positive electrode, BF.sub.4.sup.-, ClO.sub.4.sup.- or I.sup.- can be doped between graphite layers during charging and such ions are removed by discharging, thus producing reversible charge-discharge cycles. However, the negative ions doped between graphite layers repel each other and this puts limits on the amount of negative ions that can be doped electrochemically. Furthermore, the cell produces an energy density as low as 100 W.h/kg and no higher energy densities can be obtained. If graphite is used as the negative electrode, positive ions such as Li.sup.+ ions can be doped between graphite layers but such positive ions are very unstable within the liquid electrolyte and will easily react with it.
The use of activated carbon fibers as the material for the two electrodes is disclosed in Japanese Patent Application (OPI) Nos. 58-35881 and 59-149654. But the cells using such electrode materials generate an electromotive force as low as 1.2 to 2.9 volts. The cells have low energy densities while experiencing high self-discharge after charging.
Japanese Patent Application (OPI) No. 58-93176 proposes a cell configuration that uses as the material for both electrodes a carbonaceous pyrolyzed polymer. But this cell produces low electromotive forces in the range of 1.2 to 1.4 volts and their short circuit current is as low as 30 .mu.mA to 4 mA. Additionally, the cell has a fairly low energy density.
The use of an electroconductive polymer (e.g., polyacetylene or polyparaphenylene) as an electrode material is reported in Kotai Butsuri (Solid-State Physics), 17 (12), 753 (1982). When polyethylene was used as the material for both electrodes, the cell generated an electromotive force of 2.5 volts, an energy density of 150 W.h/hr and a maximum power density of 17 kW/kg. When a negative electrode made of metallic lithium and a positive electrode made of the polymeric material were used, the respective cell parameters were 3.5 volts, 290 W.h/kg and 3.5 kW/kg. In spite of these good values for cell performance, polyacetylene is unstable and is highly sensitive to oxidative deterioration, causing adverse effects on the cell performance such as cycle life. Furthermore, polyacetylene and polyparaphenylene are not easily dissolvable or meltable and cannot be shaped into various forms of electrodes by ordinary methods.